Airborne vehicles, such as helicopters and vertical and/or short take-off and landing (V/STOL) may be used to carry, e.g. hanging by wires, cargo hanging beneath the body or fuselage of the vehicle. Such cargo may be referred to as a slung load or a sling load. If the airborne vehicle utilizes a RAdio Detection and Ranging (RADAR) altimeter to measure the vehicle's height above terrain, the sling load can interfere with the operation of the RADAR altimeter by presenting a false indication of range to, or height above terrain. RADAR altimeter may also be referred to as a Radio Altimeter.
Complex techniques have been proposed to avoid such a false indication, such as by adjusting the direction of the emitted RADAR altimeter signal, desensitizing a portion of the signal return resulting from the sling load, or placing a passive modulator on the sling load to indicate its presence. A RADAR altimeter signal return, or return signal, may otherwise be referred to herein as a reflected signal.
These techniques are either costly to implement and/or may affect the ability of the RADAR altimeter to accurately detect the height above terrain. Therefore, there is a need for a cost-effective RADAR altimeter that does not diminish the accuracy or sensitivity when measuring height above terrain in the presence of a sling load.